Nature might abhor a vacuum, but Seattle is embracing the void -- at least for the coming week, when the Emerald City hosts the 2007 annual meeting of the American Vacuum Society. I'm in town to cover one small aspect of the conference, the Industrial Physics Forum (IPF), organized this year around the theme of meeting future energy needs, with sessions on hydrogen and fuel cell automobiles, solid state lighting, photovoltaics, biomass, wind and geothermal energy sources, and an entire session on nuclear power (both conventional and the fusion-based ITER facility now under construction). Things will be a bit quiet at the Cocktail Party this week, since I'll be blogging the IPF sessions, along with some representatives from the Society of Physics Students. It's a continuation of last year's blogging experiment, except I've learned not to promise live blogging, after the dismal wireless access I encountered at the 2006 IPF conference. Feel free to pop on over and check out what's going on over the next few days.
I'm hoping the IPF doesn't keep me so busy that I miss out on the special exhibit on vacuum history -- and this being a physics blog, you know I don't mean Hoovers. (It's a common mistake: the AVS has fielded so many calls from people looking for repair information on their vacuum cleaners that one year, they made up buttons and stickers featuring a vacuum cleaner in the middle of a red circle with a line through it, a la Ghostbusters.) Because I love physics history, and vacuum technology has some pretty fascinating tales buried amongst all the usual tedium. Vacuum technology in general has become so commonplace in science, it kinda gets taken for granted. But it's a crucial enabling component to so much of modern-day science and technology, from incandescent light bulbs, vacuum tubes, and industrial manufacturing to double-paned windows, thermos bottles, vacuum packing, even giant particle accelerators like Fermilab's Tevatron, or the Large Hadron Collider.
The standard definition of a vacuum, per Wikipedia, is "a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than standard atmospheric pressure." Right away, you should see a problem with that: we now know that space can't be perfectly empty, thanks to the presence of virtual particles popping in and out of existence in the quantum vacuum on time scales so short as to be undetectable by our cutting-edge scientific instruments. But that's a "perfect" vacuum. We can certainly achieve partial vacuums, and have done so for millennia. It's hard work, though, and the lowest pressures we can currently achieve in a laboratory are about 10<-13> Torr.
The first recorded experiments on the existence of vacuum were apparently conducted by an Arab philosopher named Al-Farabi in the 9th century AD, using handheld plungers in water. That's when he realized that the volume of air would expand to fill any available space. Later scientists figured out how to create better and better artificial vacuums, thanks to the principle he delineated. Here's the basic idea: By expanding the volume of a given container, pressure is reduced and a partial vacuum is created. It's temporary and is soon filled by air pushing inside by atmospheric pressure, but if the container is repeatedly sealed, the air pumped out, expanded again, and closed off, it's possible to create a sealed vacuum chamber. Today there is a staggering diversity of approaches to vacuum pumping. It's a very lucrative industry, one of the largest market sectors of scientific instrumentation today.
Vacuum is measured in units of pressure. Technically, the standard unit of pressure is the Pascal, but scientists can't possibly let things be so simple, so they came up with a new unit for vacuum pressure, the Torr, named after 17th century Italian physicist Evangelista Torricelli, best known for inventing the barometer. (He also has an asteroid named after him.) As with many useful inventions, he wasn't actually trying to invent a barometer. He was trying to solve an intriguing conundrum, namely, how to raise water levels in a suction pump to more than 32 feet in height -- the limit pumpmakers had been able to reach using simple suction pumping. It seemed that perhaps Nature truly did abhor a vacuum, but Galileo Galilei cheekily suggested that perhaps the abhorrence only extended to 32 feet. He knew a little something about the weight of air versus other substances, and thought it might be possible to overcome the obstacle using something heavier than water.
Inspired by Galileo's insight, in 1643, Torricelli hit on the notion of using mercury, which is much heavier than water (14 times heavier, in fact), in a simple experiment: he filled a three-foot-long tube with mercury and sealed it on one end, then set it vertically into a basin of mercury with the open end submerged -- being careful, obviously, not to introduce any air bubbles into the tube. The column of mercury fell about 28 inches, leaving an empty space above its level, creating an early version of a sustained manmade vacuum! Torricelli further realized that (a) the mercury would rise to the same level regardless of how tilted the tube became because the pressure of the mercury would balance the weight of the air, and (2) the height of the column of mercury rose and fell according to changing atmospheric pressure. Voila! The first barometer.
In 1650, a German scientist named Otto von Guericke built a contraption known as the Magdeburg hemispheres -- the world's first artificial vacuum. He took two large copper hemispheres with rims that fit tightly together, sealed the rims with grease, and pumped out all the air. To do so, he had to invent a vacuum pump; his version used a piston and cylinder with flap valves, powered by people turning a crank arm that was connected to the pump. Anyway, once all the air was removed from within the hemispheres, they were still held together by the air pressure of the surrounding atmosphere because the artificial vacuum inside provided no opposing pressure to balance things out. It was a pretty powerful hold, too. Four years later, von Guericke harnessed a team of eight horses to one hemisphere of the big coppery globe, and another eight horses to the other hemisphere, and then set the horses to pulling the two hemispheres apart by moving in opposite directions -- to no avail.
News of the experiment quickly spread throughout Europe, eventually reaching the ears of Robert Boyle, founder of modern chemistry, in England. Few scientists were able to replicate von Guericke's feat because it was an expensive apparatus. (Their collective minds would boggle at the price tag for modern experiment contraptions like the LHC, LIGO and ITER.) But Boyle had the 17th century equivalent of a trust fund, being the son of the Earl of Cork, so he cheerfully set about building his own "pneumatic engine," cost be damned. To do so, he enlisted the aid of Robert Hooke of Micrographia fame, then Boyle's humble assistant. Hooke had a gift for instrumentation, which is a good thing, because Boyle's design was a clunky, difficult to operate device, and sometimes Hooke was the only one who could get the thing to work properly.
In addition to public demonstrations, Boyle conducted many different experiments to determine the properties of air, specifically how "rarefied air" affected things like combustion, magnetism, sound, barometers, and various substances. He carefully detailed his observations for posterity in a very thick book ponderously titled, New Experiments Physico-Mehcanicall, Touching the Spring of the Air, and its Effects (Made, for the Most Part, in a New Pneumatical Engine). Boyle clearly lacked the gift of catchy titles. Jen-Luc Piquant would have called it something more dramatic, like Asphyxiated! Staring Into the Void of the New Pneumatical Engine. Two of Boyle's experiments involved living creatures: one tested whether insects could fly under reduced air pressure, while another dramatically showed how crucial air can be to the survival of various creatures. Boyle used birds, mice, eels, snails and such in these experiments, placing them in the vessel of the pump and studying how they reacted as the air was slowly removed. The most famous passage described a lark's response:
"... the bird for awhile appear'd lively enough; but upon a greater Exsuction of the Air, she began manifestly to droop and appear sick, and very soon after was taken with as violent and irregular Convulsions, as are wont to be observ'd in Poultry, when their heads are wrung off: For the Bird threw her self over and over two or three times, and dyed with her Breast upward, her Head downwards, and her Neck awry."
One might be forgiven for concluding that Boyle had to be one cold bastard to stand there and watch the poor innocent lark slowly suffocate to death in the name of science. Certainly audiences found the sight extremely upsetting, so much so that by the 18th century, live animals had been replaced in most such public demonstrations by a "lungs-glass" with a small air-filled bladder inside that simulated the effects of the vacuum on living creatures. Boyle's controversial approach to experimentation was immortalized in 1768, however, by the painter Joseph Wright of Derby. His canvas, An Experiment on a Bird in the Air Pump, depicts a scientist recreating Boyle's experiment with a white cockatoo, as his children and a couple of fellow scientists look on.
Vacuums serve as asphyxiants. That's what Boyle et al. learned from their experiments, and its natural to wonder what effect the vacuum would have on human beings. Well, now we know. Humans will lose consciousness after 10 seconds or so, and die within minutes, although contrary to popular depictions in movies, the body does not explode. True, the bodily fluids, like blood, could theoretically start to boil (ebullism), but this is, apparently, unlikely, at least in outer space. And vapor pressure causes substantial bloat, but the tissues are elastic and usually expand in response, preventing gross-out "ruptures."
Unless the victim holds his breath during decompression: that would be a big mistake, since this could rupture the lungs, causing death. Or the eardrums could rupture. Or the stress will make you asphyxiate. All in all, it's best not to hold your breath. Thanks to Boyle and subsequent animal experiments (not to mention gruesome Nazi experiments in 1942 involving tortured concentration camp prisoners in Dachau), we also know that living things can recover from short exposures to the vacuum (fewer than 90 seconds); no one has yet succeeded in resuscitating victims of longer full-body exposure. According to this Website, one of NASA's test subjects was accidentally exposed to a near vacuum because of a leaky space suit back in 1965. He was conscious for 14 seconds, and was successfully revived when the vacuum chamber was repressurized, but distinctly recalled feeling the water on his tongue beginning to boil.
I'm not personally keen on staring into the vacuum void myself anytime soon, but I do think it's nice to occasionally give the technology a little bit of recognition. Without vacuum technology, our science experiments wouldn't work, there would be no thin film deposition (and no nanoscale materials), plus our lighting would be hopelessly inefficient, and we wouldn't have thermos bottles to keep our coffee hot, and our iced tea cold. The vacuum: way cooler than a Hoover and even more useful.